Russia's Defense Ministry announced Monday that pro-Moscow separatists were carrying out an offensive and fighting was underway in western parts of the besieged Ukrainian port city of Mariupol, despite a Kremlin-ordered cease-fire amid civilian evacuations.

The ministry said Russian troops would suspend fire to open a humanitarian corridor out of the encircled city of 400,000 on Monday.

Russian Defense Ministry spokesperson Igor Konashenkov accused Ukrainian forces of using a group of more than 150 civilians as human shields to fire at the separatist forces.

He said four civilians had been killed and five wounded as a result, but that the forces from the Donetsk People's Republic, part of eastern Ukraine recognized as independent by Moscow, had "liberated" around 150 civilians, taking them into territory they controlled.

The corridors will open at 10 a.m. Moscow time (7 a.m. GMT) from the capital Kyiv as well as the cities of Kharkiv, Mariupol and Sumy and are being set up at the personal request of French President Emmanuel Macron, the ministry said.

Those who leave Kyiv will be airlifted to Russia, the ministry said, adding that it would use drones to monitor the evacuation and "attempts by the Ukrainian side to deceive Russia and the whole civilized world ... are useless this time."

Both sides said the third round of talks was due at an undisclosed location in Belarus. Two previous rounds yielded little beyond pledges to open routes for humanitarian access that have yet to be successfully implemented.

On Sunday the second attempt to evacuate civilians from the southern city of Mariupol failed due to the continued Russian attacks, Ukrainian Interior Ministry adviser Anton Gerashchenko said. The port city has been under siege for a week.

"There can be no 'green corridors' because only the sick brain of the Russians decides when to start shooting and at whom," he said on Telegram.

Earlier Sunday the city council in Ukraine's port city of Mariupol said it will begin efforts to evacuate its civilian population after Saturday's attempts were scuppered by cease-fire violations.

Some of the 400,000 residents trapped by Russian forces were set to start evacuating at 12 p.m. local time (10 a.m. GMT) on Sunday under a temporary cease-fire that was to last until 9 p.m. About 440,000 people resided in the port city on the Sea of Azov before the Russian invasion. Many residents still there are without electricity, water and heat after days of Russian bombardment.

A similar plan had to be abandoned on Saturday after the cease-fire was not fully observed, with both sides trading blame. It was not clear how many civilians were able to escape during the brief window when the fighting paused. Buses had been arranged to transport people out of the besieged city.

'Russia ready to halt military action in a moment'

Russia is demanding that Ukraine cease military action, change its constitution to enshrine neutrality, acknowledge Crimea as Russian territory and recognize the separatist republics of Donetsk and Luhansk as independent territories, Kremlin spokesperson Dmitry Peskov said.

Peskov told Reuters that Russia had told Ukraine it was ready to halt its military action "in a moment" if Kyiv met its conditions.

It was the most explicit Russian statement so far of the terms it wants to impose on Ukraine to halt what it calls its "special military operation" in Ukraine, now on its 12th day.

Peskov said Ukraine was aware of the conditions. "And they were told that all this can be stopped in a moment."

On the issue of neutrality, he said: "They should make amendments to the constitution according to which Ukraine would reject any aims to enter any bloc. This is possible only by making changes to the constitution."

The Kremlin spokesperson insisted Russia was not seeking to make any further territorial claims on Ukraine. "We really are finishing the demilitarization of Ukraine. We will finish it. But the main thing is that Ukraine ceases its military action. They should stop their military action and then no one will shoot," he said.

"They should make amendments to their constitution according to which Ukraine would reject any aims to enter any bloc. We have also spoken about how they should recognize that Crimea is Russian territory and that they need to recognize that Donetsk and Lugansk are independent states. And that’s it. It will stop in a moment," Peskov said.

Russia's invasion has been condemned around the world, sent more than 1.5 million Ukrainians fleeing abroad and triggered sweeping Western-led sanctions aimed at crippling the Russian economy.

Russia calls the campaign it launched on Feb. 24 a "special military operation." It has repeatedly denied attacking civilian areas and says it has no plans to occupy Ukraine.